Mobile communication system, mobile communication method, and mobile station suitably used for the same

ABSTRACT

The object of the present invention is provide a mobile communication system which can reduce power consumption of a mobile station without increasing the number of times the data signals which are to be received by the mobile station are retransmitted. The base station  10  comprises a signal transmitter  11  configured to transmit the data signal a to the mobile station  30  within a predetermined period, and transmit each of retransmission signals a 1  to a 3  of the data signal a, in a form different from that of the data signal a, from the base station  10  to the mobile station  30  within the predetermined period A. The mobile station  30  comprises a receiving processor  31  configured to carry out receiving processing of the data signal a or the retransmission signal a 1  within the predetermined period A; a communication quality detector  32  configured to detect a communication quality of the data signal a or the retransmission signal a 1 ; and a reception processing method decider  33  configured to decide a reception processing method for the data signal a or the retransmission signal a 1  in the predetermined period A, in accordance with the communication quality detection result.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation of and is based upon and claims thebenefit of priority under 35 U.S.C. §120 for U.S. Ser. No. 10/675,967,filed Oct. 2, 2003, and claims the benefit of priority under 35 U.S.C. §119 from Japanese Patent Application No. 2002-292929, filed Oct. 4,2002, the entire contents of each which are incorporated herein byreference.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a mobile communication system whichtransmits a data signal from a base station to a mobile station, amobile communication method, and a mobile station suitably used for thesame.

2. Description of the Related Art

As shown in FIG. 1, broadcast communication whereby one or a pluralityof base stations 101 to 107 transmit common information (data signal) tounspecified mobile stations 301 to 3012 in predetermined areas all atonce is known in a conventional mobile communication system.

As shown in FIG. 2, multicast communication whereby one or a pluralityof base stations 101 to 107 transmit common information to a pluralityof mobile stations joining in (belonging to) a specific group inpredetermined areas all at once is known in a conventional mobilecommunication system.

However, there is a problem in that communication qualities of signalsreceived by the mobile stations 301 to 3012 are different from oneanother depending on a propagation distance and a propagationenvironment between the base stations 101 to 107 and the mobile stations301 to 3012, so that the number of times that the base stations 101 to107 transmit (retransmit) the common information (data signal) isincreased when retransmission of the common information is requested foreach of the mobile stations 301 to 3012, in the conventional mobilecommunication system such as the broadcast system or the multicastsystem, in which the common information is transmitted to the pluralityof mobile stations 301 to 3012.

Moreover, there is a problem in that it is necessary to carry outreception processing of a long signal containing a redundant signal forerror correction even at a mobile station in which a communicationquality of a received signal is good when the redundant signal for errorcorrection is used in order to reduce the number of times the commoninformation is retransmitted, so that power consumption of the mobilestation becomes larger in the conventional mobile communication system.

BRIEF SUMMARY OF THE INVENTION

In view of the foregoing, it is an object of the present invention toprovide a mobile communication system which can reduce power consumptionof a mobile station without increasing the number of times the datasignals which are to be received by the mobile station areretransmitted, a mobile communication method, and a mobile stationsuitably used for the same.

A first aspect of the present invention is summarized as a mobilecommunication system which transmits a data signal from a base stationto a mobile station.

The base station comprises a signal transmitter configured to transmitthe data signal to the mobile station within a predetermined period, andtransmit each of retransmission signals of the data signal, in a formdifferent from that of the data signal, from the base station to themobile station within the predetermined period.

The mobile station comprises a receiving processor configured to carryout receiving processing of the data signal or the retransmission signalwithin the predetermined period; a communication quality detectorconfigured to detect a communication quality of the data signal or theretransmission signal; and a reception processing method deciderconfigured to decide a reception processing method for the data signalor the retransmission signal in the predetermined period, in accordancewith the communication quality detection result.

A second aspect of the present invention is summarized as a mobilecommunication method for transmitting a data signal from a base stationto a mobile station.

The method comprises the steps of (A) transmitting the data signal fromthe base station to the mobile station within a predetermined period,and transmitting each of retransmission signals of the data signal, in aform different from that of the data signal, from the base station tothe mobile station within the predetermined period; (B) carrying outreceiving processing of the data signal or the retransmission signalwithin the predetermined period in the mobile station; (C) detecting acommunication quality of the data signal or the retransmission signal inthe mobile station; and (D) deciding a reception processing method forthe data signal or the retransmission signal in the predeterminedperiod, in accordance with the communication quality detection result inthe mobile station.

A third aspect of the present invention is summarized as a mobilestation for receiving a data signal from a base station.

The mobile station comprises a receiving processor configured to carryout receiving processing of the data signal or a retransmission signalof the data signal within a predetermined period; a communicationquality detector configured to detect a communication quality of thedata signal or the retransmission signal; and a reception processingmethod decider configured to decide whether or not to receive the datasignal or the retransmission signal in the predetermined period, inaccordance with the communication quality detection result.

A fourth aspect of the present invention is summarized as a mobilestation for receiving a data signal from a base station. The mobilestation comprises a receiving processor configured to carry outreceiving processing of the data signal or a retransmission signal ofthe data signal within a predetermined period; a communication qualitydetector configured to detect a communication quality of the data signalor the retransmission signal; and a reception processing method deciderconfigured to decide whether or not to decode the data signal or theretransmission signal in the predetermined period, in accordance withthe communication quality detection result.

In the third or fourth aspect, the communication quality detector maydetect at least one of a signal-to-interference ratio (SIR) and areceived power as the communication quality.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

FIG. 1 is a diagram showing an entire configuration of a mobilecommunication system for carrying out broadcast communication accordingto a prior art.

FIG. 2 is a diagram showing an entire configuration of a mobilecommunication system for carrying out multicast communication accordingto a prior art.

FIG. 3 is a diagram showing a configuration of a mobile communicationsystem according to an embodiment of the present invention.

FIG. 4 is a diagram showing data signals and retransmission signalstransmitted from a base station of the mobile communication systemaccording to the embodiment of the present invention.

FIG. 5 is a flowchart showing operation of the mobile communicationsystem according to the embodiment of the present invention.

FIG. 6 is a flowchart showing operation of the mobile communicationsystem according a modified example 1 of the present invention.

FIG. 7 is a flowchart showing operation of the mobile communicationsystem according to a modified example 2 of the present invention.

DETAILED DESCRIPTION OF THE INVENTION

<A Configuration of a Mobile Communication System of an Embodiment ofthe Present Invention>

A configuration of a mobile communication system according to anembodiment of the present invention will now be described with referenceto FIGS. 3 and 4. A mobile communication system 1 according to thisembodiment transmits data signals from a base station (transmitter) 10to a mobile station (receiver) 30.

As shown in FIG. 3, the base station 10 includes a signal transmittingunit 11. The signal transmitting unit 11 is configured to transmit thedata signals and retransmission signals of the data signals to themobile station 30 within a predetermined period. The data signals andthe retransmission signals may be generated at a radio control unit (notshown) or the base station 10.

For example, as shown in FIG. 4, the signal transmitting unit 11transmits a data signal a, a retransmission signal a1 of the data signala, a retransmission signal a2 of the data signal a, and a retransmissionsignal a3 of the data signal a in this order to the mobile station 30within a predetermined period A.

The retransmission signals a1 to a3 of the data signal a are generatedby copying the data signal a.

The signal transmitting unit 11 may transmit each of the retransmissionsignals a1 to a3 in a form different from that of the data signal awithin the predetermined period A.

For example, the signal transmitting unit 11 can transmit theretransmission signals a1 to a3 of the data signal a and the data signala as different encoding series by changing rate matching parametersbetween the retransmission signal a1 to a3 of the data signal a and thedata signal a.

As shown in FIG. 3, the mobile station 30 includes a receptionprocessing unit 31, a communication quality detecting unit 32, and areception processing method deciding unit 33.

The reception processing unit 31 is configured to carry out receptionprocessing of the data signals or the retransmission signals within thepredetermined period, based on a reception processing method decided bythe reception processing method deciding unit 33.

Specifically, the reception processing unit 31 includes a receiving unitand a decoding unit. The receiving unit is configured to receive thedata signals or the retransmission signals transmitted from the basestation 10. The decoding unit is configured to decode the received datasignals or the received retransmission signals.

More specifically, the receiving unit of the reception processing unit31 determines, in the predetermined period A, whether or not to receiveeach of the data signal a, the retransmission signal a1, theretransmission signal a2, and the retransmission signal a3, based on thereception processing method decided by the reception processing methoddeciding unit 33.

The decoding unit of the reception processing unit 31 determines, in thepredetermined period A, whether or not to decode each of the data signala, the retransmission signal a1, the retransmission signal a2, and theretransmission signal a3, based on the reception processing methoddecided by the reception processing method deciding unit 33.

When each of the retransmission signals a1 to a3 of the data signal a istransmitted in a form different from that of the data signal a withinthe predetermined period A, the reception processing unit 31, forexample, carries out rate matching by using different parameters betweenthe retransmission signals a1 to a3 of the data signal a and the datasignal a to synthesize codes of the retransmission signals a1 to a3 ofthe data signal a and the data signal a.

The communication quality detecting unit 32 is configured to detect acommunication quality of the data signal or the retransmission signal.For example, the communication quality detecting unit 32 detects atleast one of a signal error, a signal-to-interference ratio (SIR) and areceived power as the communication quality.

The reception processing method deciding unit 33 is configured to decidea reception processing method for the data signal or the retransmissionsignal in the predetermined period in accordance with a communicationquality detection result detected by the communication quality detectingunit 32.

Specifically, when the communication quality result of the data signal asatisfies a desired communication quality, the reception processingmethod deciding unit 33 decides to change the reception processingmethod which is to be used by the reception processing unit 31.

On the other hand, when the communication quality result of the datasignal a (or retransmission signal a1 or the like) does not satisfy thedesired communication quality, the reception processing method decidingunit 33 receives the next retransmission signal a1 (or retransmissionsignal a2 or the like).

The reception processing method deciding unit 33 may decide thereception processing method based on a communication quality of acurrent signal or based on a combination of the communication qualitiesof the current signal and a past signal.

For example, assuming that a current signal is the retransmission signala2, the reception processing method deciding unit 33 may decide areception processing method based on a communication quality of theretransmission signal a2, based on a communication quality of theretransmission signal a1 (past signal) and the communication quality ofthe retransmission signal a2, based on a communication quality of thedata signal a (past signal) and the communication quality of theretransmission signal a2, or based on the communication quality of thedata signal a (past signal), the communication quality of theretransmission signal a1 (past signal) and the communication quality ofthe retransmission signal a2.

<An Operation of the Mobile Communication System of the Embodiment>

An operation of the mobile communication system 1 according to thisembodiment will be described with reference to FIG. 5.

As shown in FIG. 5, in step 301, the reception processing unit 31 of themobile station 30 carries out reception processing for the data signal atransmitted from the signal transmitting unit 11 of the base station 10within the predetermined period A.

In step 302, the communication quality detecting unit 32 of the mobilestation 30 detects a communication quality (Q) of the received datasignal a.

In step 303, the reception processing method deciding unit 33 of themobile station 30 determines whether the communication quality (Q) ofthe data signal a detected by the communication quality detecting unit32 satisfies a desired communication quality.

Herein, the reception processing method deciding unit 33 may determinethat the desired communication quality is satisfied when thecommunication quality (Q) of the data signal a is equal to or higherthan the desired communication quality, or when the communicationquality (Q) of the data signal a exceeds the desired communicationquality.

When the communication quality (Q) of the data signal a satisfies thedesired communication quality, the reception processing method decidingunit 33 adaptively changes the reception processing method in step 304.

On the other hand, when the communication quality (Q) of the data signala does not satisfy the desired communication quality, the operationreturns to step 301, where the reception processing unit 31 carries outthe reception processing for the retransmission signal a1.

Thereafter, in step 302, the communication quality detecting unit 32detects a communication quality of the received retransmission signala1. In step 303, the reception processing method deciding unit 33determines whether the communication quality (Q) of the retransmissionsignal a1 satisfies the desired communication quality.

When the communication quality (Q) of the retransmission signal a1satisfies the desired communication quality, the reception processingmethod deciding unit 33 adaptively changes the reception processingmethod in step 304.

On the other hand, when the communication quality (Q) of theretransmission signal a1 does not satisfy the desired communicationquality, the operation returns to step 301, where the receptionprocessing unit 31 carries out the reception processing for theretransmission signal a2. Thereafter, similar processing is repeated forthe retransmission signals a2 and a3 within the predetermined period A.

A MODIFIED EXAMPLE 1

The present invention is not limited to the above embodiment and can beapplied to the following modified example 1.

As shown in FIG. 6, in step 401, the reception processing unit 31 of themobile station 30 carries out reception processing for the data signal atransmitted from the signal transmitting unit 11 of the base station 10within the predetermined period A.

In step 402, the communication quality detecting unit 32 of the mobilestation 30 detects a “signal error (signal error rate or amount ofsignal error)”, a “signal-to-interference ratio” or a “received power”of the data signal as the communication quality (Q) of the received datasignal a.

For example, the communication quality detecting unit 32 detects a“signal error” by determining with an error detection bit in the datasignal (e.g., CRC bit) whether or not the data signal is an error.

In step 403, when it is determined that the communication quality (Q) ofthe data signal a satisfies the desired communication quality, thesubsequent retransmission signal a1 is not necessary, so that thereception processing method deciding unit 33 turns off the receiver ofthe reception processing unit 31.

MODIFIED EXAMPLE 2

The present invention is not limited to the embodiment as describedabove and can be applied to the following modified example 2.

As shown in FIG. 7, in step 501, the reception processing unit 31 of themobile station 30 carries out the reception processing for the datasignal a transmitted from the signal transmitting unit 11 of the basestation 10 within the predetermined period A.

In step 502, the communication quality detecting unit 32 of the mobilestation 30 detects a “signal error (signal error rate or amount ofsignal error)”, a “signal-to-interference ratio” or a “received power”of the data signal as the communication quality (Q) of the received datasignal a.

In step 503, when it is determined that the communication quality (Q) ofthe data signal a satisfies the desired communication quality, theretransmission signal a1 for correctly decoding the data signal a is notnecessary, so that the reception processing method deciding unit 33turns on the decoding unit of the reception processing unit 31.

<Functions and Effects of the Mobile Communication System According tothe Embodiment>

According to the mobile communication system of this embodiment, thesignal transmitting unit 11 of the base station 10 transmits the datasignal a and the retransmission signals a1 to a3 within thepredetermined period A, and the reception processing method decidingunit 33 of the mobile station 30 decides the reception processing methodfor the data signal a or the retransmission signals a1 to a3 in thepredetermined period A in accordance with the communication qualitydetection result of the received signal, so that it is possible toreduce the power consumption of the mobile station 30 without increasingthe number of times the data signals are retransmitted from the basestation 10 to the mobile station 30.

As described above, according to the present invention, it is possibleto provide the mobile communication system which enables a reduction inpower consumption of the mobile station without an increase in thenumber of times the data signals which are to be received by the mobilestation are retransmitted, the mobile communication method, and themobile station suitably used for the same.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and the representative embodimentshown and described herein. Accordingly, various modifications may bemade without departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

1. A mobile communication system which transmits a data signal from abase station to a mobile station, wherein the base station comprises asignal transmitter configured to transmit the data signal to the mobilestation within a predetermined period, and transmit each ofretransmission signals of the data signal in a form different from thatof the data signal from the base station to the mobile station withinthe predetermined period; the mobile station comprises: a receivingprocessor configured to carry out receiving processing of the datasignal or the retransmission signal within the predetermined period; acommunication quality detector configured to detect a communicationquality of the data signal or the retransmission signal; and a receptionprocessing method decider configured to decide a reception processingmethod for the data signal or the retransmission signal in thepredetermined period, in accordance with the communication qualitydetection result.
 2. A mobile communication method for transmitting adata signal from a base station to a mobile station, the methodcomprising the steps of: transmitting the data signal from the basestation to the mobile station within a predetermined period, andtransmitting each of retransmission signals of the data signal, in aform different from that of the data signal, from the base station tothe mobile station within the predetermined period; carrying outreceiving processing of the data signal or the retransmission signalwithin the predetermined period in the mobile station; detecting acommunication quality of the data signal or the retransmission signal inthe mobile station; and deciding a reception processing method for thedata signal or the retransmission signal in the predetermined period, inaccordance with the communication quality detection result in the mobilestation.
 3. A mobile station for receiving a data signal from a basestation, the mobile station comprises: a receiving processor configuredto carry out receiving processing of the data signal or a retransmissionsignal of the data signal within a predetermined period; a communicationquality detector configured to detect a communication quality of thedata signal or the retransmission signal; and a reception processingmethod decider configured to decide whether or not to receive the datasignal or the retransmission signal in the predetermined period, inaccordance with the communication quality detection result.
 4. Themobile station according to claim 3, wherein the communication qualitydetector detects at least one of a signal-to-interference ratio (SIR)and a received power as the communication quality.
 5. A mobile stationfor receiving a data signal from a base station, the mobile stationcomprises: a receiving processor configured to carry out receivingprocessing of the data signal or a retransmission signal of the datasignal within a predetermined period; a communication quality detectorconfigured to detect a communication quality of the data signal or theretransmission signal; and a reception processing method deciderconfigured to decide whether or not to decode the data signal or theretransmission signal in the predetermined period, in accordance withthe communication quality detection result.
 6. The mobile stationaccording to claim 5, wherein the communication quality detector detectsat least one of a signal-to-interference ratio (SIR) and a receivedpower as the communication quality.